It is a known fact that living organisms react defensively against implanted artificial organs or medical devices to show prominent rejections such as blood coagulation, inflammation and encapsulation. This is a result of a series of bioactivation reactions that start from adsorption of proteins on materials constituting the artificial organs and medical devices. Accordingly, treatments with such artificial organs or medical devices entail simultaneous use of drugs, for example anticoagulants such as heparin and immunosuppressants.
However, side effects of these drugs have been concerned when the treatment extends over a long period of time or as the patients grow older.
Thus, development is under way for a series of medical materials capable of solving such problems, known as biocompatible materials. Of the biocompatible materials developed so far, 2-methacryloyloxyethyl phosphorylcholine (MPC) homopolymers and copolymers with other monomers (hereinafter “MPC polymers”) show particularly remarkable biocompatibility (Ishihara et al., Polymer Journal, Vol. 22, p. 355, 1990). These polymers are developed focusing on the structure of biomembrane surfaces such that they have phosphorylcholine groups which are phospholipid polar groups.
MPC, which is a methacrylate, is water soluble as a homopolymer and can be rendered water insoluble by copolymerization with other vinyl monomers to attain suitable structures for surface treatment of the medical devices.
By coating the device surface with the MPC polymer, blood coagulation can be prevented without giving the anticoagulant, and subcutaneous implementation tests have proven very high biocompatibility (Ishihara et al., Surgery, Vol. 61, p. 132, 1999). With such properties, the MPC polymers have been used as surface-coating materials for medical devices already applied in clinical settings in the United States and Europe. The number of approvals given to such coated devices has been increasing also in Japan. These movements have created expectations that medical device effectiveness will be dramatically improved and the patients can enjoy higher quality of life.
However, resistance to heat in autoclave sterilization, hydrolysis resistance and mechanical strength are still insufficient because of the flexible main chain structures of the MPC/vinyl compound copolymers in addition to the MPC's inherent hydrophilicity. There is therefore a need for a new material that exhibits improved heat resistance, hydrolysis resistance and mechanical strength while maintaining superior biocompatibility and processability of the MPC polymers.